This invention relates to packaging of items in a film, and in particular to an improved method and apparatus for packaging groups of compressible items tightly within a film as the items are transferred from an upstream location to a downstream location.
For many years, packaging machines have been made to accumulate a number of individual items into a group for overwrapping into a bundle, most commonly within a plastic film which partially or totally envelopes the group of items. The individual compressible items may be prewrapped in film or paper, or unwrapped, such as rolls of bathroom tissue, household towels, paper napkins, or other paper products which might be part of an already formed package, or might be singly presented to be gathered in a group. Once assembled in a desired grouping, the items are then overwrapped. One such automatic bundling machine is disclosed in U.S. Pat. No. 4,679,379 to Cassoli. In this apparatus, an assembled group of items is pushed into a partially-formed package which has already been sealed and severed at one end due to a previous sealing and severing operation. As the items are pushed into the package, they contact the previous seal, and are then pushed further to impart motion to the film and the group to advance them simultaneously to a sealing and severing station. As the film is advancing a rolling sealer seals the overlap of the tube and when fully advanced the tube is sealed and severed by a sealing and severing die which seals the rear of the package just completed and the front of the next package.
As a function of the sealing and severing operation the seals must be permitted a period of time to cool under pressure to enable the seal to achieve sufficient strength before being released from the sealing and severing dies. Failure to allow such cooling to "set up" the seal may cause premature seal failure.
The Cassoli apparatus, although a viable commercial machine and process, has serious limitations which directly affect the production rate and package quality:
1. Speeds of the machine in its commercial form are typically quoted at production rates of twelve packages per minute, but rarely is this rate achieved. Since, in order to advance the film, the group of items to be packaged is pushed into the tube to the seal at its end thus unwinding the film roll and continues until the correct amount of tubing has been formed. This method produces a severe strain on the newly created end seal which requires excessive cooling and thus severely limits the production capacity of the machine.
2. Since the film is being advanced by the group of items to be packaged pushing against the end seal, it is necessary to limit the velocity of the loading apparatus to reduce the pressure on the end seal,
3. If compression of the package product is desired, the amount of compression is severely limited by the strength of the end seal as the compression method used by Cassoli is that of fixed plates which cause added friction between the compression plate and the film adding to the pressure on the end seal. Compression therefore is minimal in the width direction of the package and there is nothing in the Cassoli apparatus for compressing the package in its length direction. For these reasons, the package produced by this apparatus has a relatively loose wrap.
4. A further problem involves expelling the air that may be trapped in front of the group of items as they are being forced into the partially made package. This air may escape between the items and the film if the film is loose or breathing holes may be punched in the film, usually in the area of the gussets to allow the release of this air. These bundles are often placed in open storage and punching holes in the film renders the package non water proof.
5. In order to produce a tightly wrapped compressed package with uniform end gussets, all causes of pressurized air must be substantially eliminated, otherwise the bundle will be difficult to handle through automatic warehousing systems and present an unpleasing appearance if the bundle is in fact sold as a unit.
It is therefore important to produce a packaging apparatus which when operating at substantial rates can bundle, compress and seal items in various geometric configurations in a package which is uniform, substantially waterproof, uniform in its dimensions and aesthetically pleasing at point of sale. The present invention meets all such criteria and solves the considerable problems of the prior art, as discussed above.